1. Field of the Invention
This invention relates to fire retardant siloxane foams.
2. Description of the Prior Art
Siloxane foams are known to the art, however, these foams have not had an acceptance in commerce as has other types of foams, such as polyurethane foams. Such a siloxane foam is described by Leonard B. Bruner in U.S. Pat. No. 3,070,555 in which he describes mixing a hydroxylated organopolysiloxane containing silicon-bonded hydrogen, a hydroxylated compound and a stannous salt of a hydrocarbon-soluble carboxylic acid and thereafter allowing the mixture to foam to an elastic product. Another siloxane foam is described by Siegfried Nitzsche et al. in U.S. Pat. No. 3,338,847 in which a foam is prepared from a mixture of a linear hydroxyl endblocked diorganosiloxane polymer, an organohydrogensilicon compound, an aliphatically unsaturated organohydroxy silicon compound and a metal salt of a monocarboxylic acid. Another foam is described by Harold R. Hersh in U.S. Pat. No. 3,429,838 in which a siloxane foam is prepared by mixing a silicone rubber containing a linear, fluid methylpolysiloxane having terminal silicon-bonded hydroxyl groups, diatomaceous earth, zinc oxide, calcined clay, polyethylsilicate and tin octoate with a silicone blowing agent which was a trimethylsilyl chain-stopped dimethylpolysiloxane fluid with some of the silicon-bonded methyl groups replaced by silicon-bonded hydrogen atoms and stannous octoate catalyst.
Also known to the art are fire resistant and self-extinguishing siloxane foams. Ronald L. Joyce in U.S. Pat. No. 2,956,032 describes a fire resistant organosiloxane elastomer foam of the type described by the Bruner patent containing in addition a compound of nickelous bromide, aromatic pentabromoethylbenzene or aromatic pentabromotoluene. Siegfried Nitzsche et al. teach in U.S. Pat. No. 3,428,580 a self-extinguishing organopolysiloxane resin foam containing a resin organosiloxane polymer having alkoxy and hydroxy functionality, a fluid organohydrogen siloxane polymer, a compound having non-acidic reactive hydroxyl groups and a catalyst of quaternary ammonium compounds and carboxylic acid salts of heavy metals.
Although foams can be prepared as described above, there is a problem in use over broad temperature ranges such as from room temperature up to 300.degree. C. and when fire retardant foams are made they often give off toxic vapor ingredients when heated. Thus, a more useful elastomeric siloxane foam is desirable and one which is also non-toxic, particularly when it is fire retardant. It is known that platinum provides fire retardant properties to gum based silicone rubbers as described in U.S. Pat. No. 3,514,424 and from U.S. Pat. No. 3,652,488 that certain silicone rubbers can be made fire retardant by using a combination of platinum and carbon black. From U.S. Pat. No. 3,734,881, it is known that certain room temperature silicone elastomers, namely those containing acetoxy and ketoxime functionality, can be made self-extinguishing and non-toxic by using platinum and carbon black.
From the above prior art, siloxane foams have been prepared and fire retardant siloxane foams have been prepared, however, it was not known prior to application Ser. No. 519,380, filed Oct. 30, 1974, now U.S. Pat. No. 3,923,705 by Schuyler B. Smith and assigned to the same assignee as this application that siloxane foams could be prepared using a platinum catalyst nor was it known that such foams would be both fire retardant and non-toxic and that increased fire retardancy would be obtained by using carbon black. Smith unexpectedly found that a fire retardant foam could be obtained by using a platinum catalyst even though foams ordinarily act as very thin section materials compared to the usual solid material and it is known that the same material in thinner section will burn more rapidly than a thicker section, thus foams are generally more combustible than solid materials and it is therefore unexpected that a siloxane foam would be made fire retardant without the conventional fire retardant additives.
The foams of Smith were found to be essentially closed-cell in structure to the extent of 80 percent or more. It was totally unexpected that open-cell structure could be increased by having present in the foam mixture an organomonohydrogensiloxane.